Since the advent of optical fibers significant efforts have been underway to devise means for efficiently coupling optical signals onto a target at an economical cost. Current methods use expensive, exotic optics or difficult pigtailing techniques to couple light from a source such as a laser diode to a target such as an optical fiber or a photodetector. Such complex mechanisms, having severe tolerance requirements, are disclosed in a number of issued patents. The pigtailing techniques particularly apply to packaged laser diodes where the optical fiber is connected through an opening in the package directly to, or as close as possible to being directly to, the laser diode itself.
In order to couple light from sources such as a packaged laser diode to a target such as an optical fiber with minimal signal loss, adjustments of the positions of the components are required in all three axes. These adjustments normally require very high precision. In order to permit these adjustments, the components usually are "floating" which allows for the necessary adjustments. After determining the optimum position of the lenses used to couple light from the source to the target, the components are typically all fixed in place with respect to each other and with respect to the housing involved.
One concept that has been put forth for light coupling of this type is to use balls or spherical lenses to couple light from a source to a target. This concept has been explored in several publications and patents. Theoretical and experimental studies in the so-called "expanded beam" method have shown the deleterious effects of misalignments of the ball lenses to the optical axis. The prior art solution for compensating for the undesired offsets, which leads to loss of coupled optical signal power, lies in highly precise manufacturing tolerances.
U.S. Pat. Nos. 4,265,511 and 4,451,115, both issued to Nicia et al, disclose the use of two ball lenses for coupling optical fibers. These patents disclose the concept of carefully aligning each fiber in a tube at a precise axial and distance position with respect to its respective ball lens. The couplers of these patents only have adjustments to the axis angle of the aligned fibers in order to insure both axes are parallel. There is no provision for lateral adjustment of either ball lens with respect to its fiber. These patents indicate that even with offset but parallel fiber axes, the ball lenses will couple a significant portion of the optical signal, whereas without the ball lenses there would be substantially no coupling between the two fibers with the same offset.
Certain other patents show two ball lens coupling systems for connecting optical fibers but they do not disclose any adjustment means of the balls with respect to the fibers. These assemblies depend on manufacturing tolerances and unique methods for optimum alignment of optical fibers. These U.S. Pat. Nos. include 4,304,461, 4,371,233, 4,468,087, 4,592,619 and 4,632,505. U.S. Pat. No. 3,620,603 discloses a single ball lens system where the lens is movable, in a plane perpendicular to the optical axis. The optical source is coupled to a spherical target surface or other spherical optical collection device through the adjustable ball lens. The use of a standard cup point set screw and tension spring which acts on the side of the ball opposite to the set screw provides the physical means for adjustment. The purpose of this patent is to provide for tilting of the optical plane by relative movement between the lens and the spherical target surface, which target surface may be a bundle of optical fiber ends. The patent also suggests that the ball lens may be comprised of several elements. The purpose is to focus different objects at different distances from the ball lens at the same time, always on the same spherical target surface. There is, however, no suggestion to employ two ball lenses for this purpose. More specifically, a second ball lens would have no function in this prior art invention.